Linear Actuator

ABSTRACT

Embodiments described herein may take the form of an electromagnetic actuator that produces a haptic output during operation. Generally, an electromagnetic coil is wrapped around a central magnet array. A shaft passes through the central magnet array, such that the central array may move along the shaft when the proper force is applied. When a current passes through the electromagnetic coil, the coil generates a magnetic field. The coil is stationary with respect to a housing of the actuator, while the central magnet array may move along the shaft within the housing. Thus, excitation of the coil exerts a force on the central magnet array, which moves in response to that force. The direction of the current through the coil determines the direction of the magnetic field and thus the motion of the central magnet array.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a nonprovisional patent application of and claims the benefit to U.S. Provisional Patent Application No. 62/007,301 filed Jun. 3, 2014 and titled “Linear Actuator” and to U.S. Provisional Patent Application No. 62/044,881 filed Sep. 2, 2014 and titled “Linear Actuator,” the disclosure of each is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments described herein generally relate to actuators for producing a haptic force, and more particularly to a resonant linear actuator that moves bidirectionally in response to electromagnetic motive forces.

BACKGROUND

Many modern portable electronic devices include actuators to provide alerts and notifications. As one common example, many mobile phones include a rotary vibration motor with an eccentric weight that spins rapidly in order to produce a vibration. This vibration may alert a user to an incoming telephone call when the phone is muted, for example. The vibration takes the place of the standard audio alert and may be felt by the user if he or she is touching the phone. However, the vibration may still be noisy in certain environments and this may be undesirable.

Further, many rotary mass actuators not only create an audible buzz, but also an undesirable feel. Because rotary mass actuators spin up to an operating state and then wind down to a rest state, they constantly shake the enclosure of the electronic device. This feels “buzzy” to a user and there is little, if any, control over the haptic output of such a device other than to control the amplitude of the output or to provide discrete outputs with an unacceptably long time between the outputs.

Certain linear actuators are used instead of rotary mass actuators in some electronic devices. Linear actuators may deliver a more crisp haptic output and are quieter in certain cases. However, many such linear actuators are relatively large and some may move a mass only in a single direction.

Accordingly, an improved linear actuator may be useful.

SUMMARY

Embodiments described herein may take the form of a linear actuator capable of moving bidirectionally. Embodiments may provide a substantial haptic output resulting from relatively small motion of a mass within the actuator.

One embodiment may take the form of a linear actuator, comprising a mass assembly; a shaft passing through the mass assembly; and an electromagnetic structure operative to exert a motive force on the mass assembly, whereby the mass assembly may move along the shaft in response to the motive force; wherein the electromagnetic structure encircles at least a portion of the mass assembly when the mass assembly is in a rest state.

In certain example embodiments, the mass assembly comprises: a magnet array and a frame affixed to the magnet array; the electromagnetic structure encircles the magnet array when the mass assembly is in a rest state; and the frame extends around at least a portion of the electromagnetic structure. Further embodiments may use a wrapped coil as the electromagnetic structure, and position the coil such that it does not abut either the frame or the mass assembly.

Another embodiment may take the form of a linear actuator, comprising: a moving mass formed from a frame receiving a magnet array; a coil passing through the frame and around at least a portion of the magnet array; a shaft extending through the frame, the magnet array and the coil, the shaft spaced apart from each of the frame, the magnet array and the coil; a first spring positioned around the shaft at a first end of the shaft; a second spring positioned around the shaft at a second end of the shaft; and a case enclosing the moving mass, the coil, the shaft, and the first and second springs; wherein the shaft, the first spring and the second spring are all affixed to the case.

These and other embodiments, as well as the operations and uses thereof, will be apparent upon reading the specification in its entirety.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts a sample electronic device that may incorporate a linear actuator, as described herein.

FIG. 2 depicts a sample linear actuator, in accordance with embodiments described herein.

FIG. 3 depicts the sample linear actuator of FIG. 2 with a portion of a housing removed therefrom.

FIG. 4 depicts a cross-section of the sample linear actuator of FIG. 2, taken along line 4-4 of FIG. 3, with the flex removed for clarity.

FIG. 5 depicts a cross-section of the sample linear actuator of FIG. 2, taken along line 5-5 of FIG. 3.

FIG. 6 depicts a cross-section of the sample linear actuator of FIG. 2, taken along line 6-6 of FIG. 2.

DETAILED DESCRIPTION

Embodiments described herein may take the form of an electromagnetic actuator that produces a haptic output during operation. Generally, an electromagnetic coil is wrapped around a central magnet array. A shaft passes through the central magnet array, such that the central array may move along the shaft when the proper force is applied.

When a current passes through the electromagnetic coil, the coil generates a magnetic field. The coil is stationary with respect to a housing of the actuator, while the central magnet array and an associated frame may move along the shaft within the housing. (The frame and array together form a mass assembly.) Thus, excitation of the coil exerts a force on the central magnet array, which moves in response to that force. The direction of the current through the coil determines the direction of the magnetic field and thus the motion of the central magnet array. It should be appreciated, however, that alternative embodiments may generate a motive force through other means, such as purely through the injection of flux into the coil by operation of injector magnets as described elsewhere herein.

Generally, the central magnet array may slide along the shaft in response to the magnetic field generated by the coil. The central magnet array may be placed within, coupled to, or otherwise associated with a weight, such as a frame, that also moves with the array. The frame adds mass to the central magnet array and so may provide a greater haptic output in response to motion than would the array alone.

One or more bearings, such as jewel bearings, may form the interface between the central magnet array and the shaft. The bearings may be shaped to reduce contact between the bearing interiors and the shaft, thereby reducing friction and permitting greater, and/or higher velocity, motion along the shaft by the central magnet array. Further, the shape of the bore through the bearings reduces the likelihood that the bearings and/or shaft are constrained, thereby avoiding binding and/or friction due to misalignment of portions of the actuator.

The shaft may be affixed to the housing of the actuator at both ends. A separate spring, such as a beehive (or double beehive) spring, may encircle each end of the shaft and abut both the interior of the housing and the frame. The springs may allow the coil and array (e.g., the mass assembly) to increase an amplitude of the array's motion with each excursion from a rest state and, also may prevent the frame from hitting or crashing into the housing. Further, the springs may return the mass assembly to its rest position at or near the center of the housing. In some embodiments, the springs may cooperate with the coil's magnetic field to return the central magnet array/mass assembly to its rest position.

The frame's motion, and changes in direction of motion, is transmitted to the housing of the actuator as a force. Accordingly, as the frame moves and/or changes direction, the housing experiences forces that cause it to move. This motion may be felt or otherwise sensed by a person holding or otherwise in contact with the actuator; the motion may thus provide a haptic output sensed by the user/wearer. Typically, the greater the momentum of the central magnet array and frame, the greater the force exerted on the housing in a short period of time and the greater the magnitude of the haptic output.

Certain embodiments may employ a set of injector magnets positioned on opposing sides or faces of the frame. The injector magnets may be adjacent or otherwise near stabilization rails, which may likewise be magnetic (or, in some embodiments, may be ferritic). Magnetic attraction between the injector magnets and the stabilization rails may prevent the frame from rotating during its lateral motion along the shaft. Further, because the injector magnets and stabilization rails need not touch one another, they may not generate friction that would otherwise oppose the lateral motion of the frame along the shaft. This lack of friction may permit the frame to reach higher velocities in the same amount of travel, thereby generating a greater haptic output than if friction-inducing stabilizing structures were employed.

Generally, and as described below, the injector magnets, stabilization rails, and at least portions of the housing may create magnetic return paths that control and/or focus the magnetic flux of the central magnet array and/or the coil. These magnetic return paths may reduce the amount of flux that extends beyond the housing and thereby enhance the magnetic field within the housing that, in turn, may enhance the velocity that the central magnet array may reach within a given period of time or given distance of travel. The injector magnets (described below) may likewise exert an electromotive force on the central magnet array, enhancing or adding to that generated by the coil and thus enhancing the overall operation of the actuator.

FIG. 1 generally depicts a sample electronic device 100 that may incorporate a linear actuator, as described herein. The sample electronic device 100 is depicted as a smart phone. It should be appreciated that the sample electronic device 100 is provided as only one example of a device that may incorporate a linear actuator as discussed herein. Other sample devices include tablet computing devices, laptop or other portable computers, input peripherals (such as keyboards, mice, joysticks, track pads and the like), wearable electronic devices, including glasses, watches, health monitoring devices, and so on.

Typically, although not necessarily, the sample electronic device 100 may include a number of different components within the exterior housing 110. Sample components include one or more processing units (which may be multithreaded or multicore), memory and/or other data storage, one or more batteries, physical support structures, sensors (including position, acceleration, gyroscopic, ambient light, motion, audio, and so on), cameras, speakers, microphones, and the like. These components are not illustrated in FIG. 1 for purposes of simplicity and clarity.

Likewise, a user, wearer or other entity may access from one or more input mechanisms from outside the housing 110. For example, an input button 120 is shown in FIG. 1. Touch-sensitive surfaces, such as display 130, may also function to provide user input. These input mechanisms may be used to provide input to the electronic device 100. As one example, an input mechanism may be used to acknowledge an alert or other haptic output provided by embodiments of an actuator as described herein.

FIGS. 2-6 depict one embodiment of a linear actuator 200. It should be appreciated that the embodiment shown in FIGS. 2-6 is one sample embodiment with a sample configuration; alternative embodiments may have different shapes, structures, configurations, components and the like. Accordingly, the figures and associated discussion should be understood as examples, rather than limiting.

Turning now to FIG. 2, the linear actuator 200 may have a body 210 encompassed by a case 220. The case 220 may extend to form a bracket 230, which may connect to a housing 110 of the electronic device 100. Motion of the moving mass assembly (discussed with respect to FIGS. 3-6) may be transferred to the case 220, as described below, and through the bracket 230 to the housing 110. In this manner the moving mass assembly's motion may create a user-perceptible motion of the housing. Such motion may be selective, affecting only a portion of the housing or concentrated in a portion of the housing 110, or may broadly affect the housing as a whole. In either event, the linear actuator 200 may thus produce a haptic output that may be used as an alert or notification to a user.

The linear actuator 200 may be relatively compact, making it particularly suitable for use in small electronic devices. In one embodiment, the volume of the actuator (e.g., the volume of the case and all space inside the case) is no more than 568 cubic millimeters.

A stiffener 240 may be affixed or otherwise placed on the bracket 230. The stiffener 240 may be adhered, welded, mechanically fastened, or otherwise connected to the bracket 230. The stiffener 240 may strengthen the bracket 230. By stiffening the bracket 230, the stiffener 240 may permit more motion of the moving mass assembly and associated frame to be transmitted to the housing 110 to which the bracket 230 is affixed.

A flex 250 may extend through the case 220 to provide electrical connections for components within the case 220. Some embodiments may omit the flex 250 and may instead provide electrical contacts on the exterior of the case 220, or may use a rigid connector in place of the flex 250.

The case 220 may be formed from multiple sidewalls that are attached or affixed to one another or may be formed as an integral unit that is bent or otherwise formed into the shape of the case 220. As shown in FIG. 2, protrusions 270 formed on certain sidewalls of the case may clip or snap, be laser-welded or otherwise positioned/affixed into apertures formed on adjacent sidewalls of the case, thereby maintaining structural integrity during operation. These protrusions 270 mechanically interlock the sidewalls of the case, thereby assisting in constraining the sidewalls with respect to the housing. As also shown in FIG. 2, the bracket 230 may be unitarily formed with at least one sidewall of the case 220, although in alternative embodiments the bracket 230 may be separately formed and affixed to the case.

FIG. 3 is a three-quarters perspective view of the linear actuator 200, with a top, front and left sidewall of the case 220 removed to expose internal components. As shown in FIG. 3 and also in FIG. 6, a coil 300 encircles a central magnet array 310, which may form a moving mass assembly in conjunction with a frame 330. The coil 300 may be energized by transmitting a current along the length of the wire forming the coil; the direction of the current flow determines the direction of the magnetic flux emanating from the coil in response to the current. As discussed later, passing a current through the coil may cause the central magnet array 310 (and thus the assembly) to move along a shaft 320. In order to prevent the central magnet array 310 from being attracted to the shaft 320, which could increase friction between the two and thereby increase the force necessary to move the central magnet array 310 and frame 330, the shaft 320 may be formed from a non-ferritic material such as tungsten, titanium, stainless steel, or the like.

As depicted in FIGS. 3 and 4, the coil 300 is positioned within a frame 330 that holds the central magnet array 310, but is not affixed to the coil. Rather, an air gap separates the coil 300 from the central magnet array 310 and the frame 330 is free to move with respect to the coil 300, which is generally stationary. Further, the frame 330 generally moves with the central magnet array as part of the moving mass assembly. As illustrated in FIGS. 3 and 4, the frame may have an aperture formed therein of sufficient size to contain the coil 300. Even when the frame and central magnet array are maximally displaced within the case 220 (e.g., to one end or the other of the shaft 320), the coil 300 does not abut any portion of the frame 330. It should be appreciated that the coil 300 remains stationary in the case 220 while the frame 330 and central magnet array move, although in other embodiments the coil 300 may move instead of, or in addition to, the frame and/or central magnet array. By keeping the coil stationary, it may be easier to provide interconnections for the coil, such as between the coil and the flex, and therefore reduce the complexity of manufacture.

As shown to best effect in FIGS. 4 and 5, the central magnet array 310 may be formed from at least two magnets 400, 410 of opposing polarities. A center interface 420 may be formed from a ferritic or non-ferritic material, depending on the embodiment. A ferritic material for the center interface 420 may enhance the overall magnetic field generated by the central magnet array 310, provide at least a portion of a return path for magnetic flux and thus assist in localizing the flux within the case 220. In many embodiments, the magnets 400, 410 are neodymium while the frame is tungsten. This combination may provide a strong magnetic field and a dense mass, thereby yielding a high weight per volume structure that may be used as the moving part of the linear actuator 200.

As shown to best effect in FIGS. 5 and 6, the magnets 400, 410, frame 330, and center interface 420 may have a hole formed therethrough to receive the shaft 320. As also illustrated in FIGS. 5 and 6, the shaft generally does not touch the magnets 400, 410, frame 330 or shaft 320, all of which are supported on the shaft by the jewel bearings 430 in order to reduce friction.

Generally, when the coil 300 is energized, it creates a magnetic field. The opposing polarities of the magnets 400, 410 generate a radial magnetic field (as illustrated by the radial magnetic field 500 in FIG. 5) that interacts with the magnetic field of the coil. The Lorentz force resulting from the interaction of the magnetic fields with the current through the coil moves the central magnet array 310 and frame 330 along the shaft 320, insofar as the coil is fixed with respect to the case of the actuator. Reversing current flow through the coil 300 reverses the Lorentz force, and thus the force on the central magnet array and frame. Thus, the array and frame may move in both directions along the shaft, depending on the direction of current flow through the coil. Further, the injector magnets may also create a flux through the coil, thereby resulting in, or enhancing, a Lorentz force.

Accordingly, when the coil is energized, the central magnet array 310 will slide along the shaft 320 in one direction or its opposite, depending on the polarity of the field. If the current through the coil 300 is sufficiently high, the central magnet array and associated frame 330 will move rapidly and reach a high velocity. If the coil is de-energized before the central magnet array moves too far (for example, before the central magnet array no longer underlies the coil), then the Lorentz force exerted on the central magnet array is reduced to zero and the frame/magnet array may continue to move.

In some embodiments, after a target velocity or displacement is reached the coil may be energized in a direction opposite its energization. This may cause the generated magnetic field to exert a force in a direction opposite the initial motion of the central magnet array and/or frame, thereby slowing down or braking the moving mass assembly. This may be useful to control or limit oscillation, especially at or near a resonance frequency of the linear actuator 200, or to maintain such a resonance frequency. Accordingly, the coil 300 can not only “pull” but can also “push” the moving mass assembly, hereby imparting motive force in two opposing directions through selective application of the coil's magnetic field. This may permit fine control over motion and/or velocity of the frame 330 and central magnet array 310, both in multiple directions and when compared to other linear actuators.

Turning now to FIG. 4, the jewel bearings 430 encircle the shaft 320 and are affixed to the frame 330, thereby forming an interface between the shaft and frame. As shown in FIG. 4, the jewel bearings 430 have a generally convex inner surface to minimize contact with the shaft 320. This, in turn, may reduce or minimize friction between the jewel bearings 430 and shaft 320, such that a higher peak velocity may be reached in a set time by the frame 330 and central magnet array 310 than might be achieved if the bearings had greater surface contact with the shaft. The jewel bearings 430 are affixed to the frame 330 and move with the frame along the shaft 320.

It should be appreciated that the jewel bearings 430 may have other surface configurations designed to reduce contact and/or friction between the bearings and the shaft and to reduce the likelihood of binding and/or friction resulting from misaligned components. For example, the inner surface of the bearings may be angled, elliptical, or the like. In addition, bearings other than jewel bearings 430 may be used in different embodiments.

The shaft 320 has been generally discussed with respect to the motion of the central magnet array 310 and frame 330. The shaft 320 may be affixed to opposing sidewalls of the case 220, as generally shown in FIG. 5. As also shown in FIG. 5, in some embodiments the shaft 320 may extend through one or more sidewalls of the case 220. In other embodiments, the shaft 320 may be fully contained within the case.

Generally, the shaft passes through the central magnet array 310, including the center interface 420 and both magnets 400, 410. The shaft 320 likewise passes through the frame 330, which is affixed to the central magnet array (and, in some embodiments, more particularly to the magnets 400, 410). The shaft extends through a spring 510 at either of the shaft's ends before passing through the case 220, or otherwise being affixed to the case 220.

Typically, although not necessarily, the shaft 320 defines a central axis along one direction of the linear actuator 200. As illustrated in FIG. 5, the shaft 320 is centrally positioned within the linear actuator 200 and runs parallel to a longitudinal axis of the linear actuator 200 (e.g., left to right in the position shown in FIG. 5). The shaft need not be coincident with a center axis of the linear actuator 200, but in some embodiments such coincidence facilitates even distribution of mass about the shaft in order to maximize a haptic output of the linear actuator 200.

As previously mentioned and as also illustrated in FIG. 5, each end of the shaft 320 passes through a spring 510. In the embodiment shown in FIGS. 2-6, each spring 510 is a double beehive spring. In many embodiments, the double beehive spring shape serves multiple purposes, including: providing a large working travel range while collapsing to a small size, thereby enhancing overall possible displacement of the moving mass assembly; distributing stresses, thereby enabling the springs themselves to be smaller than may otherwise be the case; and/or centering the spring ends on both an end plate and the bearing, thus avoiding or reducing friction resulting from coils rubbing on the shaft or housing.

The double beehive springs 510 typically abut or are affixed to both an inner surface of the case 220 and a side of the frame 330. Thus, as the frame 330 and central magnet array 310 move along the shaft in response to a Lorentz force generated through the interaction of the magnetic flux of the central magnet array and the current through the coil, one double beehive spring 510 structure expands and one compresses from its nominal rest state. When fully compressed, the windings of the double beehive spring 510 lie flat within a plane. The pitch between the windings of the spring may vary in order to accommodate the windings in a flat, coplanar position upon compression. Further, by sizing both springs to always be in compression, the springs act intandem to double the spring rate. Additionally, the compression springs may not require attachment or affixing to a sidewall or other part of the actuator, thereby avoiding possible complexities, variability and stresses caused by such attachment.

Accordingly, the double beehive spring 510 may be space-efficient and designed to occupy a minimum volume when fully compressed. By reducing the volume or the springs when in a compressed state, or at least their thickness along a dimension parallel to the shaft 320, the distance the moving mass assembly may move along the shaft, the size of the central magnet array 310, and/or the amount of mass may be increased when compared to a spring that does not collapse to place its windings within a plane.

The springs 510 may prevent the frame 330 from impacting a sidewall of the case 220 when the frame 330 moves at a high velocity or enjoys a large displacement. Further, the coil 300 may be energized in order to move the frame 330 and central magnet array 310 along the shaft 320, thereby further compressing one of the springs 510. (It should be appreciated that the springs 510 are always in compression in the depicted embodiment). Current may be maintained through the coil 300 to bias the central magnet array 310 and frame 330 into a displaced position, thereby further compressing a spring 510 and storing energy in the spring. When current to the coil is terminated, the external force exerted on the central magnet array 310 may likewise terminate. In response the spring 510 may expand, propelling the moving mass assembly away from the spring 510 and along the shaft 320. Current may flow through the coil 300 at the appropriate time to impart more motive force to the moving mass assembly, thereby increasing the velocity of the assembly and enhancing the haptic output generated by this moving element. Accordingly, the springs 510 may be used to convert kinetic energy to potential energy, thereby enabling the actuator to achieve a greater amplitude of momentum across multiple cycles of operation, and so create an enhanced or increased haptic sensation for a user or wearer when compared to the haptic sensation that may be (at least initially) experienced if the moving mass assembly is in the neutral, or rest, position as illustrated in FIG. 5.

Embodiments of a linear actuator 200, as described herein, may include one or more injector magnets 600, as shown in FIGS. 2-6 generally and specifically discussed with respect to FIG. 6. Each injector magnet 600 may be affixed to a side of the frame 330, and may be positioned such that a back side of the injector magnet is near an outer surface of the coil 300, but separated therefrom by a gap (which may be an air gap). An outer surface of each injector magnet 600 may be curved or otherwise arcuate, or may be angled, taper to a point, elliptical, or the like; the injector magnets may likewise be shaped to increase or decrease the stabilization provided by the injector magnets, as generally discussed below.

A pair of rails 610 may be affixed to an interior of the case 220 and positioned such that each rail 610 is generally near an injector magnet 600. The rails 610 may be magnetic, in which case their polarities match the polarities of the nearby injector magnets (e.g., magnetic attraction exists between each rail 610 and the nearby injector magnet). Alternatively, the rails 610 may be made of a ferritic material but may not be magnets themselves, such that the injector magnets 600 are attracted to the rails 610. In alternative embodiments, the rails 610 may be magnetic and the injector magnets may be replaced with ferritic masses. The arrows shown on the injector magnets and rails in FIG. 5 indicate the direction of magnetic flux through the magnets and rails, respectively.

The injector magnets 600 serves three purposes, namely to stabilize the moving mass assembly during motion along the shaft, such that the assembly does not rotate substantially about the shaft, to provide additional flux through the coil 300 (and so increase the motive force acting on the moving mass assembly) and also to provide a magnetic flux path for the magnetic fields generated by the coil and central magnet array. The first purpose will be initially discussed. It should be appreciated that the double-headed arrow shown in FIG. 6 illustrates potential rotational motion of the central magnet array and frame about the shaft; this is the rotational motion that is resisted by the injector magnets and rails 610.

The convex shape of the injector magnet 600 helps ensure that the outermost part of the injector magnet 600 (e.g., the part closest to the rail 610) is attracted to the rail 610. Further, if the frame 330 assembly rotates or spins about the shaft 320 during movement such that it is angularly misaligned, the convex shape of the exterior portion of the inject magnet reduces the likelihood that the injector magnet will be attracted to any ferritic or magnetic portion of the case 220, as compared to an injector magnet having a rectangular or square cross-section. Rather, the attraction between the injector magnet 600 and rail 610 tends to maintain the injector magnet's alignment with respect to the rail 610 in such a manner that the injector magnet remains substantially parallel to the rail 610, in the position shown in FIG. 6. Thus, even if the frame and injector magnets become rotationally misaligned about the shaft, the injector magnets 600 operate to realign the frame, central magnet assembly and themselves with respect to the rails 610 and thus with respect to the shaft. The injector magnets essentially provide roll stability for the moving parts of the actuator and may permit implementation of non-axially-symmetric actuator sections that are stable without requiring addition mechanical constraints, which generally may occupy volume within the actuator and/or may add friction to the system.

This self-realigning action may prevent the frame 330 from binding on the shaft 320 and may maintain the frame and central magnet array 310 in a position with respect to the shaft that is configured for low-friction and/or lower-power motion of the frame along the shaft. Further, because the injector magnets 600 do not physically contact the rails 610, there is no friction between the two, thereby reducing the overall friction of the system while maintaining the roll stability and self-aligning features of the moving parts of the actuator (e.g., injector magnets 600, frame 330, and central magnet array 310).

Because the strength of a magnetic field varies non-linearly with the distance between two magnets, or a magnet and a ferritic material, the stabilization provided by the injector magnets 600 and rails 610 is non-linear. That is, the closer the injector magnets 600 are to their stable position (e.g, the position illustrated in FIG. 6), the stronger the force maintaining them in that stable position. Accordingly, even if the moving parts of the actuator become misaligned, any oscillation or motion that brings the injector magnets 600 near the rails 610 will cause the injector magnets 600, and thus the frame and so on, to quickly return to the stabilization position.

It should be appreciated that alternative embodiments may use a repulsive magnetic force, rather than an attractive magnetic force, to center the moving parts of the linear actuator 200 and prevent roll around the shaft 320. For example, magnetic rails 610 of polarities that oppose the polarities of the injector magnets 600 may be placed at the top and bottom of the case, substantially in vertical alignment with the injector magnets or along the joinder of the top of the case to a sidewall. Such magnetic rails 610 may repulse the injector magnets and cooperate to maintain the injector magnets in a stable position, so long as the strength of the magnetic fields is appropriately configured. Accordingly, embodiments are not limited to employing an attractive magnetic force to provide centering and stabilization.

The case 220 may be formed entirely from non-ferritic materials in certain embodiments, while in other embodiments the case 220 may be formed from a combination of ferritic and non-ferritic material. As one example and returning to FIG. 2, the case 220 may have a segment 280 that is ferritic in order to provide a return path through the case 220 for magnetic flux. The segment 280 may take the form of a cross as illustrated in FIG. 2. Further, the segment 280 may extend downwardly along sidewalls of the case 220 to enhance the flux return pathways. As another example, the segment 280 may be a stripe running substantially parallel to the shaft and may extend downwardly to the points at which the case 220 is affixed to the shaft.

The flux return path serves to contain the magnetic flux and prevent leakage substantially beyond the case 220 of the linear actuator 200. For example, the radial magnetic field 500, shown in FIG. 5, may extend through and be bound by the ferritic portions of the case 220 to complete a loop to the outer edges of the magnets 400, 410. Another sample flux return path may be formed through the injector magnets 600, the rails 610, and along the ferritic parts of the case 220. Generally, then, the case 220 may be configured to facilitate the formation of magnetic circuits that define flux return paths. These flux paths may also facilitate efficient transfer of energy to the moving mass, thereby increasing its velocity and haptic output during operation.

In some embodiments, the frame 330 is formed from a ferritic tungsten alloy to another flux return path and also maintain a volume-to-mass efficiency (e.g., high mass per unit volume).

Although embodiments have been described herein with respect to particular structures, circuits and operations, it should be appreciated that alternative embodiments may vary any or all of the foregoing. For example, more than two magnets may be used to form the central magnet array. Likewise, multiple coils may be used to enhance electromotive force operating on the central magnet array. The width and/or shape of either or both of the central magnet array and the coil may be varied to adjust or change a force vs. distance profile of the actuator. In still other embodiments, additional magnets may be placed at either end of the case, such that the central magnet array and/or frame pass between these additional magnets while moving. The additional magnets may be polarized to provide a restoring force that assists in moving the frame and/or array back to its rest position. In still other embodiments, the coil may be flat (e.g., planar), rather than wound around the central magnet array.

Accordingly, the proper scope of protection is defined by the appended claims and is not limited to any particular example set forth herein. 

We claim:
 1. A linear actuator, comprising: a mass assembly; a shaft passing through the mass assembly; and an electromagnetic structure operative to exert a motive force on the mass assembly, whereby the mass assembly may move along the shaft in response to the motive force; wherein the electromagnetic structure encircles at least a portion of the mass assembly when the mass assembly is in a rest state.
 2. The linear actuator of claim 1, wherein: the mass assembly comprises: a magnet array; and a frame affixed to the magnet array; and the electromagnetic structure encircles the magnet array when the mass assembly is in a rest state; and the frame extends around at least a portion of the electromagnetic structure.
 3. The linear actuator of claim 2, wherein: the electromagnetic structure is a wrapped coil; and the coil does not abut either the frame or the mass assembly.
 4. The linear actuator of claim 3, wherein: the coil generates an electromagnetic field when a current is applied to the coil; a Lorentz force results from the generation of the electromagnetic field; and the Lorentz force moves the magnet array while the coil remains stationary.
 5. The linear actuator of claim 3, wherein: a first air gap separates the wrapped coil and the mass assembly; a second air gap separates the wrapped coil from the frame; and the first and second air gaps are on opposing sides of the wrapped coil.
 6. The linear actuator of claim 2, further comprising a bearing affixed to the frame and slidably engaging the shaft, such that the frame does not directly contact the shaft.
 7. The linear actuator of claim 5, wherein an inner surface of the bearing is convex.
 8. The linear actuator of claim 2, further comprising a case containing the shaft, the mass assembly and the electromagnetic structure.
 9. The linear actuator of claim 8, wherein at least a portion of the case is formed from a ferritic material, thereby defining at least a portion of a magnetic flux return path.
 10. The linear actuator of claim 9, wherein the case reduces a leakage of magnetic flux during operation of the linear actuator.
 11. The linear actuator of claim 9, wherein a second portion of the case is formed from a non-ferritic material.
 12. A linear actuator, comprising: a moving mass formed from a frame receiving a magnet array; a coil passing through the frame and around at least a portion of the magnet array; a shaft extending through the frame, the magnet array and the coil, the shaft spaced apart from each of the frame, the magnet array and the coil; a first spring positioned around the shaft at a first end of the shaft; a second spring positioned around the shaft at a second end of the shaft; and a case enclosing the moving mass, the coil, the shaft, and the first and second springs; wherein the shaft, the first spring and the second spring are all affixed to the case.
 13. The linear actuator of claim 12, wherein; the first spring is operative to compress in response to motion of the mass assembly in a first direction; the second spring is operative to decompress in response to motion of the mass assembly in the first direction; the second spring is operative to compress in response to motion of the mass assembly in a second direction; and the first spring is operative to decompress in response to motion of the mass assembly in the second direction.
 14. The linear actuator of claim 13, wherein the first and second springs are double beehive springs.
 15. The linear actuator of claim 14, wherein the spring windings are completely coplanar when fully compressed.
 16. The linear actuator of claim 12, further comprising a flex circuit extending through the housing, the flex circuit operative to supply power to the coil.
 17. The linear actuator of claim 12, further comprising a bracket contiguously formed with the case, the bracket coupling the case to a housing of an associated electronic device.
 18. The linear actuator of claim 17, further comprising a stiffener attached to the bracket, the stiffener operative to enhance transmission of haptic output from the actuator to the housing of the associated electronic device.
 19. The linear actuator of claim 12, further comprising: a first injector magnet positioned at a first side of the frame and affixed to the frame; and a second injector magnet positioned at a second side of the frame and affixed to the frame.
 20. The linear actuator of claim 19, further comprising: a first rail affixed to a first interior side of the case, the first interior side of the case facing the first side of the frame; and a second rail affixed to a second interior side of the case, the second interior side of the case facing the second side of the frame.
 21. The linear actuator of claim 20, wherein the first and second injector magnets are magnetically attracted to the first and second rails, respectively.
 22. The linear actuator of claim 21, wherein the attraction between the first injector magnet and first rail, and the attraction between the second injector magnet and second rail, provide rotational stability to the moving mass during motion of the moving mass. 